Weak, frictionally unstable input sediments explain shallow seismogenesis at the north Sumatran subduction zone

Stanislowski, Katja, Hüpers, Andre, Fagereng, Åke ORCID: https://orcid.org/0000-0001-6335-8534 and Ikari, Matt J. 2025. Weak, frictionally unstable input sediments explain shallow seismogenesis at the north Sumatran subduction zone. Geology 10.1130/G52910.1

Preview

PDF - Published Version Available under License Creative Commons Attribution. Download (1MB) | Preview

Abstract

The cause of unexpectedly shallow seismic slip during the 2004 Sumatra-Andaman earthquake, which resulted in a devastating tsunami, is still under debate. One hypothesis is that diagenetic strengthening of décollement-forming input sediments prior to subduction allows shallow seismogenic behavior. We tested this hypothesis by measuring the frictional behavior of input sediments, sampled offshore northern Sumatra during International Ocean Discovery Program (IODP) Expedition 362, in single-direct shear experiments. The input sediments that have been correlated with the north Sumatra proto-décollement horizon are frictionally unstable, indicating a seismogenic shallow décollement. These sediments are also frictionally weak, which deviates from expected friction systematics but means that diagenetic strengthening is not required. Our observations indicate that threshold concentrations of amorphous silica (≥11 wt%), palagonite rims on glass fragments, and feldspar interspersed within weak, smectite-bearing sediments entering the north Sumatra subduction zone may cause the incoming sediments to be frictionally unstable before subduction. This instability led to the unexpectedly shallow coseismic slip during the 2004 Sumatra-Andaman earthquake and may be valuable information for hazard assessments of other subduction margins.

Item Type:	Article
Date Type:	Published Online
Status:	In Press
Schools:	Schools > Earth and Environmental Sciences
Publisher:	Geological Society of America
ISSN:	0091-7613
Date of First Compliant Deposit:	14 February 2025
Date of Acceptance:	23 January 2025
Last Modified:	19 Feb 2025 12:01
URI:	https://orca.cardiff.ac.uk/id/eprint/176191

Actions (repository staff only)

Edit Item